The main objective of our work is to determine certain structural features of the chromosome; primarily the relationship of DNA and histone. The specific goal of one study is a further definition of the conformation, distribution of bases and sequences, and flexibility of DNA in chromatin. We rely on sensitive derivative-absorption melting experiments and actinomycin D binding, the latter to exploit the well documented requirements of this drug for tight binding. Melting curves are analyzed for base composition from the well-known dependence of Tm on the fraction of G-C base pairs; and from the ratio of the derivative melting profiles at 284 nm and 260 nm. A semiquantitative analysis of the base sequence of chromatin subunit DNA for the extent of similarity to whole chromatin is made by comparison of their derivative melting profiles. One object is to determine whether chromatin formation involves condensation of DNA with regard for base composition or sequence, or to the spacial arrangement of charged phosphates on the DNA backbone. The latter would suggest the spacing of subunits in the chromosome is fixed by histones. It would also provide for rearrangement of the subunits in regions of active gene expression. The binding studies are designed to elucidate something of the flexibility of the DNA in chromatin. We imagine that the tertiary structure of DNA may impose "mechanical" constraints that limit its flexibility. This work continues with experiments to establish the existence of kinks in the DNA, and whether such kinks are thermodynamically predisposed at critically placed sequences or base pairs. The specific goal of another study is to develop a sensitive analytical probe of chromatin structure based on the kinetic behavior of calf liver type-2 cytoplasmic protein kinase which phosphorylates certain seryl residues of the histones. Phosphorylation is measured by the activity of covalently attached 32p after a 1' incubation. Substrates include purified H1, H2A and H2B, native chromatin and chromatin subunit particles from calf thymus.